87
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How many times do you have to circle the Earth to break orbit?
This depends on how much thrust you have available. With enough thrust, you don't need to be in Earth orbit at all: you can launch straight into an escape trajectory.
New Horizons did this, more or ...
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78
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Shouldn't space junk fall back to Earth on its own? How long will take for a ~1 cm piece of junk in LEO to fall back to Earth on its own for example?
It depends on the altitude. Here is a chart from ESA and UNOOSA. Basically, anything under 500 km will fall relatively quickly, maybe 25 years. Everything under 800 km should fall within a century or ...
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71
votes
Where does space begin on planets without atmospheres?
Yet surely nobody would classify Neil Armstrong's lunar bunny-hops as suborbital spaceflights.
Why not? There's no essential difference between a high-eccentricity trajectory with an apolune of 1 ...
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67
votes
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Why can't you travel to Mars in a straight line?
Only answering your first question here, and in qualitative terms:
You can't travel to Mars in a straight line for the same reasons you can't throw a ball in a straight line: gravity. If you wanted to ...
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66
votes
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What is the farthest artificial satellite in orbit in our solar system?
The term for orbits in our solar system around the Sun is Heliocentric.
Closed Heliocentric Orbit
The solar observation probe Ulysses is the furthest artificial satellite around the sun. It's in a ...
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64
votes
Why aren't the 'bedrooms' aboard the ISS also the escape pods?
Primarily, because without a lot of extra equipment, they could at best be space coffins for the astronauts.
First, they share life support with the rest of the station. Air circulated through them ...
- 54.4k
60
votes
Why are all space initiatives designed to get to space overnight when in Nature all extreme feats are achieved in a gradual process
Imagine you have a very heavy book and a bookcase, and your goal is to put the book on the top shelf of the bookcase. How much time would you spend doing that? Maybe five seconds, maybe fifteen. Would ...
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56
votes
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What does the Sun-Earth-Moon system look like from the Sun-Earth L-2 point?
I treated this as a problem of geometry and came up with this:
The sun is the large yellow disk.
The earth is the largest black disk, obscuring most of the sun
The left-hand dark-grey disk is the ...
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51
votes
Why are all trajectories in space a conic sections?
Not all trajectories in space are conic sections, only those that are a two body problem. One planet in orbit around a star is a two body problem. Only two body problems are solved by a conic section.
...
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47
votes
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Do you need 0 km/s velocity to crash into the sun?
Wouldn't i inevitably spiral to sun surface even if i was faster than 0km/s ?
No. On reasonable timescales, an orbit will have a fixed distance of closest approach, called "periapsis." (These ...
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46
votes
How many times do you have to circle the Earth to break orbit?
Zero
See at: https://en.wikipedia.org/wiki/Escape_velocity for theory.
Once you build enough velocity to surpass gravitational attraction, you will leave planetary orbit. A spacecraft simply ...
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45
votes
Escaping moons conflict with what I understand of gravity
A very good question!
The reason is essentially to do with tides. And a slightly over-simplified summary is: If the moon orbits more slowly than the rotation of the parent body (as our Moon does, 12 ...
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45
votes
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Are all satellites of all planets in the same plane?
Most large regular satellites orbit in the equatorial plane of their planet. Every planet spins, and thus has an equatorial bulge caused by centrifugal forces that over time aligns the satellites' ...
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42
votes
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Why use a retrograde orbit?
Retrograde orbits have multiple use-cases. First of all you should note that "retrograde" doesn't mean 180° inclination - everything > 90° is considered retrograde. This places all sun-synchronous ...
- 6,906
41
votes
If the Earth spun clockwise, how would that affect Space Exploration?
Primarily, locations of spaceports would change. California, not Florida would host the NASA's main launch site. Russia would be in slightly better position, able to send rockets over the Black Sea, ...
- 54.4k
37
votes
Do simulator games use a realistic trajectory to get into orbit?
I understand the reasons behind each of this manouveurs, however I'm wondering if this is how real rockets get into orbit.
Cutting off the engine and letting the rocket loose vertical speed looks ...
- 166k
36
votes
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How does a Spacecraft change its orbit?
To answer your title question: By using its engines.
However you seems to be quite puzzled by the fact that velocity of an object can decrease and increase over the course of an orbit.
If the orbit ...
- 12.6k
35
votes
Where does space begin on planets without atmospheres?
Ultimately, "the edge of space" is an agreed upon convention. In other words it is essentially arbitrary, something which only humans even care about (well maybe space aliens too <grin>). Yes, ...
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35
votes
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Do simulator games use a realistic trajectory to get into orbit?
Physics
In regards to the physics, KSP is fairly realistic, other than it not modeling n-body physics (which isn't really relevant in scope of orbiting Earth/Kerbin).
In regards to the engineering, ...
- 466
33
votes
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How is the altitude of a satellite defined, given that the Earth is not spherical?
update: 6378.137 km is what I use now.
By convention the altitude of a spacecraft is the distance to the center of the Earth minus roughly 6378 kilometers, or some reference radius that is ...
- 149k
33
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How did the USSR track Gagarin's Vostok-1 orbital flight? Was tracking capability an issue in the choice of orbit?
The Answer is on a page by Sven Grahn.
No ocean going tracking ships were used. Only ground stations on the territory of the USSR.
In the other answers some russian sources about the use of tracking ...
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33
votes
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What causes a satellite's orbit to decay?
If satellites are truly far beyond the atmosphere, their orbits do not decay, except for very small perturbation effects like solar radiation pressure from the Sun or tidal forces from the Moon.
But ...
32
votes
Why did the X-15 not achieve orbit?
You're confusing units. The maximum speed of the X-15 was 7274 km/h, or about 2 km/s. Orbital speed is around 8 km/s. The X-15 didn't carry enough fuel to reach orbital speed.
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32
votes
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Why is 51.8° inclination standard for Soyuz?
As Baikonur is at 45.965° north latitude, it would make sense if 45.965° was the standard inclination for Soyuz (and for the ISS). That would be a launch due east, thereby taking the greatest ...
- 72.6k
30
votes
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Why are the GPS constellation satellites in such a high orbit?
The main reason they are in such a high orbit is to allow for more of the Earth to be visible at any one time. In order to have a reasonable amount of the Earth visible, you have to be high up. A ...
- 121k
30
votes
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This orbit looks wrong near a Lagrange point. Is it?
Is the orbit shown in the graphic wrong, or is my understanding of orbital mechanics lacking, having only been influenced by KSP?
It's not an either-or question.
The graphic is "wrong" from the ...
- 72.6k
30
votes
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Teleporting an object into geosynchronous orbit
I'm afraid you are incorrect. An object on the equator of Earth has a velocity of ~460 m/s. A satellite in geosynchronous orbit has a velocity of ~3000 m/s.
You may be confused by the fact that both ...
- 177k
30
votes
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How far have astronauts been in space?
Twelve Apollo astronauts landed on and walked on the Moon
Twelve more Apollo astronauts orbited the Moon without landing
So that's twenty-four individuals that count towards "(except for the ...
- 149k
28
votes
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The Loose Astronaut
This is a great question. I wanted to provide an answer which cited some specific, real-world situations. Currently the only people in space are those aboard the International Space Station. If anyone ...
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28
votes
How does a planet's gravity push away smaller bodies that would otherwise intersect its orbit?
I feel the need to correct some issues that were brought up in the other answers.
Yes, gravity is an attraction-only force.
But due to its relative weakness, objects in space can attain large ...
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